1. Field of the Invention
The invention relates to a novel virus composition useful for protecting agricultural commodities from insect pests and preparation thereof.
2. Description of the Art
Baculoviruses, in particular nuclear polyhedrosis viruses (NPVs) and granulosis viruses (GVs), have many characteristics which make them particularly suitable for control of insects. NPVs and GVs are specific in their pathogenicity to the class Insecta and many are highly virulent to their hosts (Baculoviruses for Insect Pest Control: Safety Considerations, Ed. M. Summers et al., American Society for Microbiology, Washington, D.C., p. 7, 1975). Such viruses can be used to control insects which infest agricultural commodities such as the Indianmeal moth, the raisin moth, the almond moth, the tobacco moth and the like. A major problem in the use of baculoviruses to control insects is the lack of methods to readily produce large quantities of virus at low cost.
The problem of protecting agricultural commodities from insects is illustrated with reference to the Indianmeal moth, Plodia interpunctella (Hubner) (Lepidoptera: Pyralidae), hereinafter IMM. This insect is recognized as a major insect pest that infests grains, dried fruits and nuts, and other stored commodities worldwide. Presently, there is no protection for commodities such as dried fruits and nuts from IMM invasion or damage after the commodities have left the processing plant, and it has been estimated that over 90% of the losses caused by insects to dried fruits and nuts after processing are due to IMM. One problem in controlling IMM is that it has shown resistence to certain chemical insecticides, thus other possible control agents are being investigated.
Granulosis virus (GV) isolated from IMM is a highly virulent insect specific virus; it has been shown to be an effective protectant against IMM for stored dried nuts (Hunter et al., Journal of Invertebrate Pathology 22: 481 (1973) and Journal of Economic Entomology 70: 493-494 (1977)), raisins (Hunter et al., Journal of Stored Products Research 15: 65-69 (1979)), and wheat and corn (McGaughey, Journal of Economic Entomology 68: 346-348 (1975)). Because GV is unique to insects and does not infect man, it offers potential for use as a protectant against IMM on food commodities.
Until 1979, formulations of the IMM granulosis virus (IMMGV) were produced by rearing IMM larvae infected with GV on a diet and removing the infected larvae by hand from the diet. After removal, a given number of infected larvae were homogenized in distilled water to free the virus from the insect bodies, and the virus was used immediately. Alternatively, hand-collected larvae were freeze-dried and then homogenized and suspended in water just prior to use. The primary deficiency of this method was that hand-removal of the larvae from the rearing diet was tedious and time consuming and made this method of control of IMM on commodities economically unfeasible. Further, these wet formulations had the problems that loss of activity of the labile nonoccluded infectious components occurred, and the preparation process had to be repeated whenever inoculum was required.
Cowan et al., Journal of Economic Entomology 79: 1085-1090 (1986) described a freeze-dried formulation of IMMGV. This formulation was prepared by rearing GV-infected IMM larvae on a diet, and homogenizing the larvae in the diet to obtain a composition containing GV-infected larvae plus the diet components. The composition was freeze-dried, milled, and formulated with a carrier, and the formulation tested for control of IMM on almonds and raisins. The diet components used to rear the IMM larvae consisted of wheat bran, honey, water, glycerol, a vitamin mixture, and fungicides/fungistats. The problems associated with this composition (GV-infected larvae plus diet components) are that the presence of honey and glycerol caused the formulations after freeze-drying to be sticky and difficult to mill as well as hygroscopic. Attempts to minimize these problems included washing the formulation several times prior to homogenizing and freeze-drying. However, even with several washings, not all the glycerol and honey was washed out. In addition to adding additional labor with attendant increased costs, the washing procedure resulted in significant losses in potency of the formulation.